


Demonic Dynamic

by DarkAlchemistNinja, RaijiMagiwind



Category: Ao no Exorcist | Blue Exorcist
Genre: Complicated Demonic Logistics, Confusing Love Triangles, Demonic Powers, Dom/sub, Explicit Sexual Content, M/M, Multi, Polyamory, Sibling Incest, Yaoi
Language: English
Status: In-Progress
Published: 2015-04-29
Updated: 2015-07-14
Packaged: 2018-03-26 09:12:11
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 4
Words: 4,327
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/3845338
Author URL: https://archiveofourown.org/users/DarkAlchemistNinja/pseuds/DarkAlchemistNinja, https://archiveofourown.org/users/RaijiMagiwind/pseuds/RaijiMagiwind
Summary: <blockquote class="userstuff">
              <p>In the world of Blue Exorcist, Rin and Yukio are trying to comprehend, control and understand their demonic powers; Unfortunately for Yukio this means a complicated network of strange relationship rules; He's barely able to tolerate his own demonic powers, much less have to deal with the dynamics of tiered dom/sub relationships that seem to be the basis for all demonic sexual activities... not to mention demons don't really give a shit if they're related to who they decide they want to screw around with.</p>
            </blockquote>





	1. Blue Fire

**Author's Note:**

> Sooo I've never written Blue Exorcist fanfiction before... I apologize in advance if any of my information is inaccurate... don't hesitate to tell me (i know my co-author wont lol)

It was bordering on evening and Yukio Okumura was searching for his brother. It wasn't exactly an unusual thing as of late... Rin ran off and hid or went to the roof to think. It was becoming a more often occurence however. Yukio was a bit curious as to why. He sighed and closed his eyes, trying to sense his brothers' demonic energy; sealed as it was.   
The roof. Yukio sighed. "Why does it always have to be the roof?" he muttered as he went to the top floor of their dorm and climbed the ladder to the flat rooftop. "RIN!" he called as he got up there. "Rin where the hell are you?" "Go away, Yukio." came the irate response from even higher up. Fantastic, his brother was on the peak of the roof, Kuro laying beside him. 

"Rin I'm not leaving." He called up at him. "Come down from there." "NO. I said leave me alone!!" He snapped harshly, his tail lashing in annoyance. Yukio was slightly taken aback at the tone, but he was determined. "You have homework to do!" "Screw you and your damn homework!" Was the reply. "Excuse me, mister exorcist wannabe, but if you want to keep the Vatican off your ass you'll get down here and do your homework!" Said Yukio, becoming a bit irate now himself.   
"What the hell does homework have to do with me being an exorcist wannabe?" he yelled, unaware that Yukio had decided to do something stupid and try to climb up to where his brother was perched precariously. He edged out onto the ledge and started to climb the roof tiles, slipping a bit now and then. "Because if you don't know your damn scripture then you're gonna be outta luck at some point, please Rin, come down." He had gotten high enough to where he could reach out and grab at Rin's lashing tail. 

Rin hissed as an unfamiliar feeling shot through him when Yukio touched him. He jerked away, pulling Yukio off-balance and making his brother slide down the side of the roof. Luckily he managed to stay on it and not injure himself. "Damnit Rin!" he yelled. "I said leave me alone!" Rin shot back, standing up. He was glowing a faint blue despite the fact that his sword was sealed.   
Yukio blinked. Well that can't be good. Rin glared at him. "Just fuck off, alright!" He yelled, turning and jumping off the roof, running away to hide in an abandoned classroom. Rin curled up in the corner and hugged his knees, trembling a bit. He didn't like this... he didn't like it at all... He was feeling strange lately, his power kept flaring out of his control even when the sword was sealed shut. The last thing he wanted was to hurt someone and give the Vatican a damned reason to lock him up. 

Sighing, Yukio somehow managed to get off the roof without injuring himself greatly. He got a few scrapes but otherwise was fine. He tended to them for a moment before once again chasing after Rin. Something was wrong... he had to find out what and try to help. Meanwhile Rin could feel yet another flare hitting him. He was feeling wierd... and whenever he looked at Yukio the feeling got stronger. It scared the crap out of him. Did he want to hurt his brother? no... that wasn't it... then what the hell was it?

~~~~~~~~~~

It took him another twenty minutes before he felt Rin's latest flare up, and by the time he got to the classroom Mephisto was already there with at least five others of his exorcist team. Mephisto gazed at Yukio. "We've got the power contained, but i don't know how long it's going to last." he said calmly. "you should go talk to him." Yukio nodded and knocked on the door. "Rin... Rin it's me... please let me in..." he called. 

There was no answer aside from an animalistic growl. Yukio sighed and opened the door. He was immediately shocked at the state the room was now in. Fire everywhere; the wooden desks had been reduced to either rubble or ashes. Rin was in the corner of the room, his eyes shut tight as he clung to himself, his tail lashing, his fire emanating from him wildly even though he was clinging to the sword.   
Yukio steeled himself and walked directly into the flames. He felt no pain, just a plesent warmth onhis body. He approached Rin slowly, like he would a frightened and injured animal. Kuro was kept outside with the rest, perfectly fine with that because honestly Rin was scaring him too. Yukio finally got to Rin and reached out a tentative hand to touch his arm. Rin reacted instinctively; though certainly not in the way Yukio expected. 

Instead of attacking him, Rin looked at Yukio and was suddenly struck with an urge to climb into his younger brothers' lap and nuzzle him like a cat. Before he knew what he was doing he'd shifted and was curled up in Yukio's arms. The younger twin was completely befuddled. He gazed at Mephisto, who was now standing at the door observing. "ok... what?" he said in confusion.   
Mephisto stifled a snort. "Oh, so that's what this is about." he commented idly. "What? What is what what's about?" Demanded Yukio in annoyance. Mephisto took two steps and Rin glared at him and growled, so he stepped back till Rin seemed to calm down. This just confused Yukio more. 

"What is happening to your brother is something all demons go through at various times... He's in heat... and by his behavior... he's chosen you to help him deal with it." Yukio stared at him. "Hes _WHAT_!" He shrieked, horrified. "Are you telling me that Rin wants to ..." "-Yes... essentially." responded Mephisto calmly. "I'm his damned brother for godssake!" Retorted Yukio in general panic. "With demons that particular factor doesn't matter." he said matter-of-factly. "He has chosen you... If you don't comply, He'll go further out of control and quite possibly cause severe property damage, not to mention be dragged off to the Vatica-" "alright I GET IT." said Yukio in resigned exhasperation.

While this conversation was taking place, Rin had been nuzzling and pawing at Yukio, trying to take his shirt off. Yukio kept resisting for the moment. "fine.. If i have to do this..." he said, inwardly disgusted with himself but willing to do anything to keep his brother from destroying things and getting into trouble; "you will need to strengthen the wards around this room, my demon side will probably rise up and you'll have to contain us both. And for the love of all that is holy would you please refrain from telling anyone about this?" 

Mephisto nodded "you have my word." he promised. At that moment Rin glared at Mephisto and growled loudly. "alright, i'm going, i'm going!" he said, putting his hands up in surrender. "you might want this, however." he said, tossing a small sachel to them as he beat a hasty retreat. The door shut and Yukio looked at Rin, who gazed up at him with a desperate pleading look on his face. Yukio looked down at him and nodded. "I know, Rin... and I'm here for you." he said quietly, giving his permission. Rin pinned him to the floor.


	2. Domination And Submission

**Summary for the Chapter:**

> Yukio's demon side accepts Rin's domination.

**Notes for the Chapter:**

> Gah another short chapter...  
> I WILL GET THE HANG OF THIS EVENTUALLY!

Yukio let out a soft noise at the pin, but didn't struggle. He gazed up at his brother, who had desperate heat in his gaze. 

The next thing he knew Rin was kissing him and something primal deep down within his body reacted, his power flaring instantly and twining with Rin's. His eyes closed and Rin began to kiss down his neck.

A low moan tore from Yukio that sounded anything but like his normal self. Something in him knew what Rin was about to do and his body relaxed. 

Rin shifted and pulled Yukio's shirt off, unintentionally tearing it a little bit. He then bent over his younger twin and bit his shoulder, using his powers and Yukio's blood to mingle together to leave a permanant mark.

This would signal to other demons that Yukio belonged to him... and if anyone else tried to touch him... there would be ... problems.

Yukio moaned at the bite and shuddered as he felt their power combine and a bit of Rin's heat drifted into his consciousness. 

He opened his eyes a little bit, escaping the pin long enough to pull Rin's shirt off and bite down in return on Rin's shoulder. 

A different sort of mark appeared that sealed him into the role of Rin's primary submissive partner. 

His human consciousness was attempting to revolt against the union. 

_I just became my brother's mate? is that what just happened?_

**Yes.** retorted his demon half. **deal with it.**

Then he was lost again as Rin pinned him back onto the floor, his tail lashing as he kissed him deeply once again, his free hand shifting to pull at Yukio's pants, undoing the button and zipper, easing them down a little bit.

Yukio arched up a little unconsciously to make it easier on Rin as he shifted his pants down the rest of the way and tossed them aside, leaving Yukio laying there among the flames in his boxers and nothing else. 

Rin smiled at the sight of his brother in utter submission under him, wreathed in flames, both Yukio's own power and Rin's mingling together. 

The look of bliss on Yukio's face as Rin gently paused at the freshly made dominant mark on his brother's shoulder made Rin shudder in anticipation. 

He vaguely recalled the sachel the damn Clown had thrown at them and reached for it; it seemed to be fire proof. 

Rin opened it to find a small bottle of lubrication. He had the decency to blush. 

Well then... Someone truly understood what had to happen. Too bad it was the damn Clown. 

Yukio opened his eyes a little bit to watch Rin and bit his lip. 

Rin was distracted from examining the bottle at the adorable expression on Yukio's face and set the bottle down. 

Swiftly removing Yukio's boxers and the rest of his own clothes he rendered them both naked rather swiftly, and went back to kissing him, his hand drifting to gently paw at Yukio's length teasingly, earning a moan from his brother and making him grin. 

Yukio arched into the teasing, panting, his demonic side desperate by now for the touches, but his inner human screaming that _This Is So WRONG!_

But nevertheless he was moaning without shame like a horny little demonic slut, his body language begging for more. 

Rin was more than happy to oblige. He shifted a hand down under Yukio, who instinctively had shifted his body to give Rin easier access to him, and teased around his entrance, prodding at it and making Yukio gasp and bite his lip again. 

That action seemed to be a trigger that just made Rin want Yukio more.

He withdrew his hand and grabbed the lubricant, rubbing some on his fingers before going back to tease him again. 

He slowly thrusted a finger inside him.


	3. First Climax

**Summary for the Chapter:**

> Rin and Yukio consummate their demonic dominant/submissive bond

**Notes for the Chapter:**

> I'm aware it's short, it'll get longer after this methinks.

Ecstasy shot through Yukio and he arched into it, moaning softly and grinding down instinctively on the intrusion, giving his demonic side full control for the moment, His own blue flames bursting forth even more and mingling with Rin's, causing a surge of power to strain at the confinements of the seals Mephisto and the others were putting up. 

Yukio's blue flames created the beginnings of horns on his forhead but otherwise just wreathed the two of them in their mingling powers. He moaned softly as he felt Rin's finger go in and out of him and panted a bit, his body, with the surrender of his human consciousness, hungered for more. 

Rin smiled as he felt their powers join as one and purred softly, adding another finger into Yukio's tight entrance, wanting to prepare him as much as he could; the last thing he wanted to do was hurt his new submissive. 

He kept doting on his little brother, teasing him gently with his free hand, kissing him all over, wherever he could reach. He finally captured Yukio's lips again with his own and gently maneuvered a third finger inside him, so he could properly stretch him.

Yukio writhed under Rin's ministrations, panting and moaning shamelessly. He reached out and gently stroked Rin's tail, which got him a loud shuddering moan coming from Rin, so he did it again. 

He ground down on the fingers that teased him and found himself desperately wanting more, wanting Rin to stop teasing him and fill him up already. "m-more.." he panted softly, trying to hint to Rin that he was ready. 

Rin chuckled a bit, it was a rather creepy sound; at the soft whimper of Yukio writhing and begging for more. He was more than inclined to give him more. He withdrew his fingers; noting the whine Yukio made at the removal of the pleasure, and grabbed the lube again, this time coating his hard erection with it. 

He shifted and gazed at Yukio, positioning his brother properly so he'd be comfortable and Rin could have easy access to him. He aligned himself and slowly pressed his hard rod into Yukio, moaning softly as he did so; the tight wet heat surrounding it and shooting pleasure through his body. 

Yukio let out a loud shameless moan as he felt Rin fill him up; He did feel mild pain, but his demon side didn't care about that; in fact it just made the pleasure more intense. The sensation was strange but oh damn it it felt good. 

Once Rin was fully sheathed inside him he paused, panting and letting Yukio get accustomed to the sensation. He gazed down at his new Sub, pleased and eager to make him scream. It was torment to not immediately start thrusting deep into him.

Yukio panted for a second and then looked up at Rin's eager face; He was as relaxed and ready as he could be for the moment. He nodded slowly at Rin, knowing exactly what his Dom wanted, giving his permission. 

Rin immediately began to thrust into him, hard and fast; he had wanted to start slow but he couldn't help himself. Yukio milked him just right and he was desperately in heat. The moans that came from his Submissive were absolutely intoxicating, and they swiftly escalated to screams as Rin pounded into him. 

It wasn't long before Rin found Yukio's prostate and began to slam against it, causing the younger half-breed to arch and grasp at the floor, nails scratching the wood as pleasure shot through him in even greater intensity as Rin kept up his furious pace. 

They went at it for at least ten minutes before Yukio felt his climax rise like a tidal wave in his body, knotting in his gut and spreading. He cried out softly to Rin; "I'm gonna..!" 

Rin slammed into him twice more before Yukio's orgasm hit him hard and he pretty much levitated off the floor as his body went ridged and his vision went white, spraying his nectar all over his stomach as he tried to breathe. 

As Yukio's inner muscles contracted with the orgasm Rin felt his own trigger and he climaxed deep inside Yukio, filling him up with pent up seed, his own body arching and a loud scream tearing from him. 

As they both began to come down from their bliss, Rin pulled out and collapsed next to Yukio. They were both panting and pink, the flames dying down as their passion dwindled. 

Mephisto at that point stole into the room; noting that the twins were both completely out of it, and teleported them back to the dorm, settling them on the king-sized bed in the dorm President's room so they could still be together. 

Before Yukio drifted off he gazed at Rin, his senses coming back to him as his demon side retreated. "this changes nothing." he muttered, even though he knew it wasn't true. 

"yeah.. whatever... I'm taking a nap." replied Rin, cuddling closer to Yukio and falling asleep. Yukio fell asleep soon after.


	4. Denial and Desperation

**Summary for the Chapter:**

> Yukio is struggling to accept himself, and his feelings... and Rin thinks the solution is simple... however his 'simple' solution makes things far more complicated than he anticipated...
> 
> (am I getting better at these summary thingies?)

**Notes for the Chapter:**

> Sorry that i haven't updated this one in SO long, but the truth is I kinda got stuck on where to go from last chapter, since me and my co-author have done a few arcs and neither of us were sure where I should go from there, but I think i have a good idea now of how i want to continue this so hopefully I'll be updating it more often!

Things went rather uneventfully for a few weeks after that, Yukio and Rin seemed to be hot and cold, sometimes unable to stop staring at each other and at other times fighting so badly that once in a while Mephisto had to be called in to tear them apart. It was clear Yukio was fighting with himself and poor Rin was caught in it, mainly because he already accepted that part of him and Yukio was denying his own self.

One of the days after a fight, Yukio was walking down the hall in the dorm he shared exclusively with Rin and he paused, leaning against the wall and peering out the window a bit. His inner demon was driving him a bit batty... It wanted Rin... badly. He was pretty damn near feverish at times. He sighed. **You can't fight this forever, Yukio.** came his inner demon, sounding pretty goddamn smug. 

"like hell I can't." he said aloud, his voice dangerously venomous. 

**You can't. and you know you can't... you want to feel his arms on you. you want to feel his lips caress your heated skin... you want the fire to intertwine and make you one with him...** the voice was taunting him... unfortunately... it was right.

"SHUT UP!" yelled Yukio, slamming his hand on the wall, not realizing that he was beginning to flare up with blue flames on his forehead. "I do NOT want to have sex with my brother!"

 **oh but you do... you do so bad you can taste it... you dream about it every night, fantasize about it when you look at him. that tail... you want to tug on it and make him writhe and dominate you.**

Yukio flushed pink. "I said SHUT UP!" 

"Yukio, who are you talking to?" came a voice from down the hall.

The younger Okumura twin froze and looked down the hall, his face red as a beet. "R-Rin... how long have you been-"

"standing here?... long enough. You're fighting with your demonic self aren't you." said Rin, walking cautiously towards his agitated younger brother. "I've been there... many times... the truth is. You're never gonna get rid of him... so why bother fighting... just try and coexist with him. accept him." 

Yukio stepped back a bit and Rin stopped walking towards him. He didn't like the way Rin was approaching him, like he was a deer that was easily startled... even if it was true he didn't like it. "do you have any idea what it's telling me to do?!" 

"yes." 

"and you're telling me to accept it?!" Yukio's voice was elevating octaves with every sentence. 

Rin sighed, putting his hands forward, palm up in a gesture of helplessness. "What do you want me to say, Yukio? Whether you like it or not, we're bonded.. you are my primary submissive mate. I am your dominant mate. Demons don't care if they're related to their significant others." 

Recoiling, Yukio practically snarled his retort. "humans DO! You're my BROTHER for heaven's sake!" 

His brother shook his head. "We're both half demon, Yukio, whether you like it or not. And we already sealed the deal. You're craving me. Hell, you're in heat, Yukio. You will come to me. Whether of your own free will or your damned stubborn desperation, you will. And I'll be waiting to help you." He turned on his heel and went into the room they shared. "it's getting late, I'm going to bed." 

Yukio stared at the doorway, fuming. 

**He's right and you know it.** said the voice inside him, laughter in it's tone. 

Yukio growled; a very demonic growl at that. "go boil you're head." he said sullenly, not entirely sure if it was aimed at Rin or at his inner demon, or maybe both. He went into the bathroom and got himself ready for bed, then flopped onto his bunk, his back facing Rin, who was laying on the opposite side of the room, in his bunk, back facing the wall, watching Yukio. 

\-----------------------------------

Yukio drifted about in a fitful slumber, having dreams; very dirty dreams. He woke with a start in a cold sweat realizing he had to do SOMETHING or he'd go crazy. There were hushed voices on the other side of the room. One he identified easily as Rin, the other... 

He sat bolt upright and hit his head on the top bunk. Rubbing the bump he'd just created he grabbed his glasses and whipped his head around to stare at the two sitting on Rin's bed... or rather, the one beside Rin sitting on the ladder. 

"Oh good, he woke up. Those moans were starting to distract me from our conversation." the one Yukio was now staring at said lightly, amusement in his tone. His gaze drifted lower. "Oh dear how embarrassing for you.." his voice was wickedly gleeful. 

Yukio gazed downward, distracted from yelling at the two of them by the fact that he had a huge tent in his pants. He swore and grabbed his pillow, shoving it over his lap and blushing madly. 

Once he'd calmed enough to speak he looked to Rin. "What the hell is Amaimon doing here at two in the morning?" he demanded of his brother, not giving the King of Earth the satisfaction of a reply. 

"He came to talk to me, something about Cervantes and tests of some sort." Rin said calmly. 

"Yes, and then Rin was telling me a fascinating story about you two." added Amaimon with a provocative grin. "something about a bond sealed in fire and poor little Yukio fighting his true self?"

Yukio growled. 

Rin held up a hand. "oi now, before you jump down my throat I did it for a reason. If you won't accept me right now to help you with your heat, you have to take it out on someone, and as your dominant i have a right to choose who i allow to touch you." 

Yukio opened his mouth but all that came out was a loud and very high pitched squeak of indignation. He closed his mouth, took a breath and tried again. "excuse me? are you telling me that you chose, of all people... of all demons... _Amaimon_ to 'sate my lust'?! And to add to that, YOU'RE TELLING ME YOU CAN CHOOSE WHO I HAVE SEX WITH?!" 

Rin sighed and pinched the bridge of his nose. "Yes, Yukio my dear. That is what I am telling you. As your dominant i have to take care of you. If you sleep with Amaimon now, then you don't have to fuck me. Isn't that your entire moral dilemma at the moment? The fact that you don't want to have sex with me?"

Yukio sputtered for a few moments, unable to come up with a response. Yes that was part of the problem, Rin was his brother... it was _WRONG_ to sleep with him... right? So Rin was trying to fix it by setting him up with AMAIMON??

There was silence for a few moments, then Rin looked Yukio in the eye and the next words he spoke held such a compulsion to them that Yukio felt a primal need to obey. "Yukio, I want you to have sex with Amaimon. NOW." 

Yukio opened his mouth to protest but what came out was far less than that. "as you wish." He froze. Was that his voice? had he just said that? It wasn't possible. 

The next thing he knew, Amaimon had crawled up on his bunk and was gently running his fingers over Yukio's chest. It was at that moment Yukio lost it. Later the events of this would be foggy in his mind, but the results would end up changing his life, and his mind... his very destiny. 

He pinned Amaimon down, rolling so he was on top of him, and kissed him; not exactly gently. 

Amaimon let out a soft noise of surprise and before the Earth King could stop him, Yukio had bitten him on the shoulder, then licked it. Amaimon felt a wave of submissive pleasure jolt through him and He closed his eyes, relaxing under Yukio's dominant stance. 

Then he glanced to Rin through slitted eyes. **dammit I agreed to fuck him, not be bound to him!** he shot the thought at Rin, who laughed and shrugged. 

Rin hadn't planned for the bite either, but well... **You gonna accept it?**

Amaimon chose not to answer Rin, instead he decided he rather liked the way Yukio was treating him, continuing to kiss him and lick at him; yeah it was obvious he was a bit desperate and deprived, but he seemed to know Amaimon's triggers already. He let out a soft noise and shifted Yukio's nightshirt a bit to make a small bite of his own, cementing the bond. 

**I, Amaimon, King of Earth, accept Yukio Okumura as my dominant.** he thought softly to both of them. He then surrendered to Yukio's touch.

Yukio sensed the moment that Amaimon relaxed and got a bit more aggressive, slowly taking off Amaimon's clothing piece by piece, not exactly wishing to rip it off, and eventually letting Amaimon rid him of his own clothing. 

After a while of teasing Amaimon with bare touches and his tongue, Yukio sat back, looking down at Amaimon and realizing that the other was pretty damn cute with his eyes half open and panting like that. "want to play with me?" he asked, his voice a bit husky and raw with desire to claim Amaimon as his. 

"y-yes..." was the gasped and hushed reply. 

"then play." He said, rolling off Amaimon and laying beside him. "touch me, Ami."


End file.
